Method and apparatus for non-access stratum message processing during handover in evolved network

ABSTRACT

A method and an apparatus for non-access stratum (NAS) message processing during handover are provided. The method includes the steps of sending a first message to a radio access network node, wherein the first message including a non-access stratum (NAS) message, and receiving a second message from the radio access network node, wherein the second message comprising the NAS message and cause information indicating a handover is triggered.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/109,418, filed on Aug. 22, 2018, which is a continuation of U.S.patent application Ser. No. 14/968,465, filed on Dec. 14, 2015, now U.S.Pat. No. 10,075,880, which is a continuation of U.S. patent applicationSer. No. 14/156,184, filed on Jan. 15, 2014, now U.S. Pat. No.9,215,624. The U.S. patent application Ser. No. 14/156,184 is acontinuation of U.S. patent application Ser. No. 12/704,906, filed onFeb. 12, 2010, now U.S. Pat. No. 8,665,820. The U.S. patent applicationSer. No. 12/704,906 is a continuation of International Application No.PCT/CN2008/071970, filed on Aug. 13, 2008, which claims priority toChinese Patent Application No. 200710194669.9, filed on Nov. 29, 2007,and Chinese Patent Application No. 200710140567.9, filed on Aug. 13,2007, and Chinese Patent Application No. 200710147031.X, filed on Aug.23, 2007, all of which are hereby incorporated by reference in theirentireties.

FIELD OF THE INVENTION

The present invention relates to the field of communication, and moreparticularly to a method and an apparatus for non-access stratum (NAS)message processing during handover in an evolved network.

BACKGROUND OF THE INVENTION

The Universal Mobile Telecommunications System (UMTS) is a thirdgeneration mobile communication system adopting a Wideband Code DivisionMultiple Access (WCDMA) air interface technique, and the UMTS adopts astructure similar to that of the second generation mobile communicationsystem, including a Radio Access Network (RAN), a Core Network (CN), andUser Equipment (UE). The RAN is configured to process all functionsassociated with wireless communication. The CN is configured to processall speech calling and data connection functions in the UMTS, andperform switching and routing functions with external networks. The RANin the UMTS system is a UMTS Territorial Radio Access Network (UTRAN).

FIG. 1 is a schematic structural view of a UMTS. The UTRAN includes oneand more Radio Network Subsystems (RNSs), in which each RNS is formed byone Radio Network Controller (RNC) and one or more NodeBs. Each RNC isconnected with the CN via an Iu interface, each NodeB is connected withthe RNC via an Iub interface, and the RNCs are interconnected with eachother via an Iur interface. Each RNC is configured to allocate andcontrol wireless resources of the NodeBs connected with the RNC orassociated with the RNC, and each NodeB is configured to perform a datastream conversion between the Iub interface and a Uu interface, andmeanwhile is participated in part of the wireless resource management.

The network architecture shown in FIG. 1 is based on the architecture ofa version earlier than 3GPP Release 6. Considering the competitioncapability of the network in the future, the 3GPP has been researchingon a brand new evolved network architecture to satisfy the applicationrequirements of a mobile network in the future, which includes a systemarchitecture evolvement (SAE) and a long time evolvement (LTE) of theaccess network, and the network evolvement aims at providing a totallyIP-based network with a low delay, high data rate, high system capacityand coverage, and low cost.

FIG. 2 is a schematic architectural view of an evolved network. Thenetwork architecture includes a UE, an Evolved UMTS Territorial RadioAccess Network (E-UTRAN), and an Evolved Packet Core (EPC). The E-UTRANis formed by eNodeBs, in which the eNodeBs are connected with each othervia an X2 interface. The EPC includes a Mobility Management Entity(MME), a serving SAE gateway, and a Packet Date Network SAE gateway (PDNSAE gateway). The MME is responsible for the mobility management of acontrol plane, including managing user context and mobility status,assigning a user temporal identifier (ID), and the like. The MME isconnected with a Serving GPRS Support Node (SGSN) in an existing networkvia an S3 interface, connected with the E-UTRAN via an S1-MME interface,and with the Serving SAE Gateway via an S1-U interface. The MME isconfigured with a timer therein. The Serving SAE Gateway is responsiblefor initiating a paging for a downlink data in Idle state, managing andsaving IP bearer parameters and routing information in a network, andthe like. The PDN SAE gateway serves as a user plane anchor point amongdifferent access systems. The system shown in FIG. 2 further includes aPolicy and Charging Rule Function (PCRF) and a Home Subscriber Server(HSS).

In the evolved network architecture, a handover of X2 interfaces existsbetween the eNodeBs. If an eNodeB where the UE is currently located iscalled a Source eNodeB (S-eNB), and an eNodeB where the UE will behanded over to is called a Target eNodeB (T-eNB), the above handoverrefers a process that the UE is handed over from the S-eNB to a cellcontrolled by the T-eNB.

In actual applications, the EPC needs to send an NAS message to the UEthrough the eNodeB to realize a service corresponding to the UE, inwhich the time point and time interval for sending the NAS message varywith different services. In the prior art, there is a solution for NASmessage processing if the handover is successful. Unfortunately, if thehandover fails, no technical solution is available for enabling the EPCto send the NAS message to the UE.

Therefore, in the solution for NAS message processing in the prior art,the EPC cannot be informed timely if the handover fails, that is, the UEreturns to an S-eNB service area again, and as a result, the EPC cannotcorrectly send the NAS message to the UE.

SUMMARY OF THE INVENTION

Accordingly, the embodiments of the present invention are directed to amethod for NAS message processing during handover in an evolved network,an eNodeB, and an MME.

An embodiment of the present invention provides a method for NAS messageprocessing during handover in an evolved network, which includes thefollowing steps.

An EPC sends a direct-transfer message to an S-eNB, in which thedirect-transfer message contains an NAS message sent to a UE by the EPC.

The EPC receives a message, which indicates that the UE is being handedover, sent by the S-eNB.

The message which indicates that the UE is being handed over is a directtransfer failure message or a direct transfer response messagecontaining a cause value and the NAS message that fails to be sent.

An embodiment of the present invention provides a method for NAS messageprocessing during handover in an evolved network, which includes thefollowing steps.

An EPC receives a message which, indicates that a UE is being handedover, sent by an S-eNB, and buffers an NAS message to be sent to the UE.

If the handover fails, the EPC receives a message, which indicates thatthe UE returns to an S-eNB service area, sent by the S-eNB.

When it is necessary to send the NAS message to the UE, the EPC sendsthe NAS message to the UE through the S-eNB.

An embodiment of the present invention provides a method for NAS messageprocessing during handover in an evolved network, in which aretransmission timer is configured, and the method includes thefollowing steps.

An EPC receives a message, which indicates that a UE is being handedover, sent by an S-eNB, and starts the retransmission timer.

If the handover fails, when it is necessary to send an NAS message tothe UE after the retransmission timer expires, the EPC sends the NASmessage to the UE through the S-eNB.

An embodiment of the present invention provides an MME in an EPC, andthe MME includes a message transceiver module and an execution module.

The message transceiver module is configured to receive a message, whichindicates that a UE is being handed over, sent by an S-eNB, and transmitthe message to the execution module; receive a message, which indicatesthat the UE returns to an S-eNB service area, sent by the S-eNB, andtransmit the message to the execution module, if the handover fails.

The execution module is configured to receive the message, whichindicates that the UE is being handed over, transmitted by the messagetransceiver module, buffer an NAS message to be sent to the UE; receivethe message, which indicates that the UE returns to the S-eNB servicearea, transmitted by the message transceiver module, and send to theS-eNB the NAS message to be sent to the UE when it is necessary to sendthe NAS message to the UE.

An embodiment of the present invention provides an MME in an EPC, andthe MME includes a retransmission timer, a control module, and anexecution module.

The control module is configured to receive a message, which indicatesthat a UE is being handed over, sent by an S-eNB, and start theretransmission timer; receive a handover complete message sent by aT-eNB, and stop the retransmission timer.

The execution module is configured to resolve a timing result of theretransmission timer, and send an NAS message to the S-eNB when it isnecessary to send the NAS message to the UE after the retransmissiontimer expires, or send the NAS message to the T-eNB when it is necessaryto send the NAS message to the UE after the retransmission timer isstopped.

An embodiment of the present invention provides an eNodeB, whichincludes a detecting module, an NAS message forwarding module, and ahandover processing module.

The detecting module is configured to detect an abnormal status duringhandover of a UE, and send a detecting result to the handover processingmodule.

The handover processing module is configured to send a message to an EPCwhich indicates that the UE is being handed over, and send to the EPC amessage about a NodeB service area where the UE is currently locatedaccording to the detecting result sent by the detecting module when thehandover of the UE fails.

The NAS message forwarding module is configured to receive an NASmessage sent by the EPC, and forward the message to the UE.

An embodiment of the present invention provides an MME, which includes amessage sending module and a message receiving module.

The message sending module is configured to be used by the EPC to send adirect-transfer message to an S-eNB, in which the direct-transfermessage contains an NAS message to be sent to the UE by the EPC.

The message receiving module is configured to receive a message whichindicates that the UE is being handed over sent by the S-eNB, in whichthe message which indicates that the UE is being handed over is a directtransfer failure message or a direct transfer response messagecontaining a cause value and the NAS message that fails to be sent.

In view of the above, with the method for NAS message processing duringhandover in an evolved network, the eNodeB, and the MME provided in theembodiments of the present invention, an EPC sends a direct-transfermessage to an S-eNB, and the direct-transfer message contains an NASmessage to be sent by the EPC to a UE. The S-eNB notifies the EPC that amessage about the UE being currently handed over contains the NASmessage that fails to be sent by the S-eNB to the UE, so that the EPConly needs to buffer the NAS message when the NAS message fails to betransferred, so as to reduce the occupied EPC storage space.Alternatively, the S-eNB notifies the EPC that the UE is currently beinghanded over and notifies the EPC to buffer the NAS message to be sent tothe UE. When the handover fails, the S-eNB sends a message whichindicates that the UE returns to an S-eNB service area to the EPC, so asto enable the EPC to correctly send the NAS message to the UE.Alternatively, a retransmission timer is set and adopted. When thehandover fails, the EPC correctly sends the NAS message to the UEthrough the S-eNB after the retransmission timer expires, and when thehandover is successful, the EPC stops the retransmission timer, andcorrectly sends the NAS message to the UE through a T-eNB.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural view of a UMTS system;

FIG. 2 is a schematic architectural view of an evolved network;

FIG. 3 is a schematic flowchart of a first method for NAS messageprocessing during handover in an evolved network according to anembodiment of the present invention;

FIG. 4 is a schematic flowchart of a first preferred embodiment of theflow shown in FIG. 3;

FIG. 5 is a schematic flowchart of a second preferred embodiment of theflow shown in FIG. 3;

FIG. 6 is a schematic flowchart of the flow, when the handover issuccessful, included in the flow shown in FIG. 3;

FIG. 7 is a schematic flowchart of a second method for NAS messageprocessing during handover in an evolved network according to anembodiment of the present invention;

FIG. 8 is a schematic flowchart of a preferred embodiment of the flowshown in FIG. 7;

FIG. 9 is a schematic flowchart of a method for NAS message processingduring handover in an evolved network according to an embodiment of thepresent invention;

FIG. 10 is a schematic flowchart of a first preferred embodiment of theflow show in FIG. 9;

FIG. 11 is a schematic flowchart of a second preferred embodiment of theflow shown in FIG. 9;

FIG. 12 is a schematic flowchart of a T-eNB further receiving an NASmessage sent by an S-eNB via a tunnel in the flow shown in FIG. 9;

FIG. 13 is a schematic flowchart of a first preferred embodiment of theflow shown in FIG. 12;

FIG. 14 is a schematic flowchart of a second preferred embodiment of theflow shown in FIG. 12;

FIG. 15 is a schematic flowchart of the first preferred embodiment ofthe S-eNB sending an NAS message to a UE when the handover fails in theflow shown in FIG. 12;

FIG. 16 is a schematic flowchart of the second preferred embodiment ofthe S-eNB sending an NAS message to a UE when the handover fails in theflow shown in FIG. 12;

FIG. 17 is a schematic structural view of a first type of MIME in an EPCaccording to an embodiment of the present invention;

FIG. 18 is a schematic structural view of a second type of MIME in anEPC according to an embodiment of the present invention;

FIG. 19 is a schematic structural view of a first eNodeB according to anembodiment of the present invention;

FIG. 20 is a schematic structural view of a second eNodeB according toan embodiment of the present invention;

FIG. 21 is a schematic structural view of a third eNodeB according to anembodiment of the present invention; and

FIG. 22 is a schematic structural view of another MME according to anembodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In order to make the objectives and advantages of the embodiments of thepresent invention more comprehensible, the embodiments of the presentinvention are illustrated below in detail with reference to theaccompanying drawings.

Firstly, a method for NAS message processing during handover in anevolved network according to an embodiment of the present invention isillustrated, which includes two specific methods.

FIG. 3 is a schematic flowchart of a first method for NAS messageprocessing during handover in an evolved network according to anembodiment of the present invention, which includes the following steps.

In step 601, an EPC receives a message, which indicates that a UE isbeing handed over, sent by an S-eNB, and buffers an NAS message to besent to the UE.

In this step, before the EPC receives the message sent by the S-eNB,this step further includes that the EPC sends a direct-transfer messageto the S-eNB, where the direct-transfer message contains the NAS messageto be sent to the UE. In this case, the message sent by the S-eNB may bea direct transfer failure message or a direct transfer response message,and the direct transfer failure message or the direct transfer responsemessage may contain a cause value, for example, the UE is being handedover, and may further contain the NAS message received by the S-eNB fromthe EPC. The NAS message may be an NAS message received from the EPCbefore the S-eNB sends a handover command to the UE, or an NAS messagereceived from the EPC after the S-eNB sends a handover command to theUE. Alternatively, after the S-eNB sends a handover command to the UE,the EPC does not send an NAS message, and the S-eNB directly sends ahandover notification message to the EPC, and in this case, the EPCdirectly acquires that the UE is being handed over.

If the handover fails, the UE returns to an S-eNB service area, and theS-eNB sends a message which indicates that the UE returns to the S-eNBservice area to the EPC.

In step 602, if the handover fails, the EPC receives the message whichindicates that the UE returns to the S-eNB service area sent by theS-eNB.

In step 603, the EPC sends an NAS message to the UE through the S-eNB,when it is necessary to send the NAS message to the UE.

In this step, after the EPC acquires that the UE currently returns tothe S-eNB service area in step 602, when it is necessary to send the NASmessage to the UE, the EPC sends the NAS message to the UE through theS-eNB. Considering the sending mode, the EPC sends to the S-eNB thedirect-transfer message containing the NAS message to be sent to the UEby the EPC, and then the S-eNB sends the NAS message to the UE by usinga Radio Resource Control (RRC) message downlink direct-transfer message.

Through step 601-step 603, the flow of the first method for NAS messageprocessing during handover in an evolved network according to anembodiment of the present invention is ended. In this flow, the S-eNBsends a handover command to the UE, that is, the NAS message processingmanner after the handover begins.

The specific interaction processes involved during the handover, forexample, sending, by the S-eNB, a handover request to a T-eNB, andperforming, by the T-eNB, an admission control, all belong to the commonsense for those of ordinary skill in the art, which are not repeated inthe above method of the embodiment of the present invention and thesubsequent descriptions.

In the first method for NAS message processing during handover in anevolved network according to an embodiment of the present invention,when the handover fails, the EPC receives the message, which indicatesthat the UE returns to the S-eNB service area, sent by the S-eNB, andsince the EPC has acquired the exact position of the UE currently, whenit is necessary to send the NAS message to the UE, the EPC sends the NASmessage to the UE through the S-eNB, thereby realizing the effect ofsending the NAS message correctly to the UE when the handover fails.

FIG. 4 is a schematic flow chart of a first preferred embodiment of theflow shown in FIG. 3, which shows a complete process from sending, bythe S-eNB, the handover command to the UE till the NAS messageprocessing after the handover begins. The flow shown in FIG. 4 includesthe following steps.

In step 701, the UE receives a handover command message sent by theS-eNB, and the message instructs the UE to complete the handoverprocess.

In step 702, the EPC sends the direct-transfer message to the S-eNB, andthe direct-transfer message contains the NAS message to be sent to theUE.

In step 703, the S-eNB founds that the UE is no longer located in aservice area of the S-eNB, and the S-eNB sends the direct transferfailure message or direct transfer response message to the EPC. Thedirect transfer failure message or direct transfer response messagecontains a cause value, for example, the UE is being handed over, andmay further contain the NAS message received by the S-eNB from the EPC.The NAS message may be received from the EPC before the S-eNB sends ahandover command to the UE, or may be received from the EPC after theS-eNB sends a handover command to the UE.

In step 704, the EPC buffers the sending of the NAS message afterreceiving the direct transfer failure message or direct transferresponse message.

In step 705, the S-eNB detects that the handover fails, or detects otherabnormal situations.

In step 706, the S-eNB initiates a handover canceling flow to the T-eNB.

In step 707, the S-eNB sends a message containing a current position ofthe UE to the EPC, that is, notifies the EPC that the UE returns to theS-eNB service area.

In step 708, the EPC sends to the S-eNB the NAS message to be sent tothe UE when it is necessary to send the NAS message to the UE.

In step 709, the S-eNB forwards the NAS message sent by the EPC to theUE by using an RRC message downlink direct-transfer message.

Step 702 may be performed before step 701, that is, there is no strictsequence relation between step 701 and step 702.

Step 706 may be an optional step, that is, this embodiment may notinclude step 706. If step 706 is included, there is no strict sequencerelation between step 706 and step 707 during execution.

In step 707, the message containing the current position of the UE sentby the S-eNB to the EPC may be an existing S1 interface message, or maybe a new message, as long as the message can be adopted to notify theEPC that the UE returns to the S-eNB service area currently. Table 1shows a format of the above message.

TABLE 1 Type Cell/Group Name Reference Symbol Description Message TypeMandatory MME Application Part Mandatory Integer, Indicating a receivingProtocol Identifier String end of messages ENodeB Identifier MandatoryInteger, Indicating identifier String of the eNodeB itself CauseOptional Integer, Indicating a cause Enumerated value

In this preferred embodiment, the S-eNB sends the message containing thecurrent position of the UE to the EPC, so that the EPC is able toacquire the position of the UE correctly when the handover fails.

FIG. 5 is a schematic flow chart of a second preferred embodiment of theflow shown in FIG. 3, which shows a process from initiating the handovertill finishing the NAS message processing after the handover begins. Theflow shown in FIG. 5 includes the following steps.

Step 801 is the same as step 701.

In step 802, the S-eNB sends a handover notification message to the EPC,so as to notify the EPC that the UE is currently being handed over.

In step 803, the EPC buffers the sending of the NAS message afterreceiving the handover notification message.

Steps 804-808 are respectively the same as steps 705-709.

Similar to the first preferred embodiment, step 805, in which the S-eNBinitiates a handover canceling flow to the T-eNB, is an optional step,and there is not strict sequence relation between step 805 and step 806.

In step 806, the same as step 707, the message containing the currentposition of the UE sent by the S-eNB to the EPC may be an existing S1interface message, or may be a new message, as long as the message canbe adopted to notify the EPC that the UE returns to the S-eNB servicearea currently. Table 1 shows a format of the above message.

In step 802, the handover notification message sent by the S-eNB to theEPC may have various formats, and Table 2 has listed one specific formatof the above handover notification message.

TABLE 2 Type Cell/Group Name Reference Symbol Description Message TypeMandatory MME Application Part Mandatory Integer, Indicating a receivingProtocol Identifier String end of messages ENodeB Identifier MandatoryInteger, Indicating the String identifier of the eNodeB Cause OptionalInteger, Indicating a cause Enumerated value

The difference between the above flow shown in FIG. 5 and that shown inFIG. 4 lies in that, in the flow shown in FIG. 5, the S-eNB directlynotifies the EPC that the UE is being handed over, rather than sendingthe direct transfer failure message or direct transfer response messageto notify the EPC that the UE is being handed over after the EPC sendsthe direct-transfer message. Thus, when the handover fails, the S-eNBdirectly notifies the EPC of the current position of the UE, which ismuch simpler than the mode of first receiving the direct transfermessage sent by the EPC and then returning the direct transfer failuremessage or direct transfer response message to notify the EPC of thecurrent position of the UE.

The flow shown in FIG. 3 may further include the processing flow whenthe handover is successful. FIG. 6 shows a complete processing flow whenthe handover is successful. The flow includes the following steps.

Steps 901-903 are the same as steps 801-803.

In step 904, the UE sends a handover acknowledgement message to theT-eNB, so as to indicate that the handover is completed.

In step 905, the T-eNB sends a handover complete message to the EPC, soas to notify the EPC that the UE has completed the handover.

In step 906, the EPC sends the direct-transfer message to the T-eNB whenit is necessary to send the NAS message to the UE, and thedirect-transfer message contains the NAS message to be sent to the UE.

In step 907, the T-eNB sends the NAS message to the UE by using an RRCdownlink direct-transfer message.

Different from the handover failure situation, if the above handover issuccessful, the T-eNB sends a handover complete message to the EPC,which is equivalent to notifying the EPC that the UE enters a T-eNBservice area currently, so as to instruct the EPC to send the NASmessage to the UE through the T-eNB.

The flows of two preferred embodiments of the above first method for NASmessage processing during handover in an evolved network according to anembodiment of the present invention have been described above.

FIG. 7 is a schematic flow chart of a second method for NAS messageprocessing during handover in an evolved network according to anembodiment of the present invention. The flow includes the followingsteps.

In step 1001, an EPC receives a message, which indicates that a UE isbeing handed over, sent by an S-eNB, and starts a retransmission timer.

In this step, before the EPC receives the message sent by the S-eNB,this step further includes that the EPC sends a direct-transfer messageto the S-eNB, and the direct-transfer message contains an NAS message tobe sent to the UE. In this case, the message sent by the S-eNB may be adirect transfer failure message or direct transfer response message. Thedirect transfer failure message or direct transfer response message maycontain a cause value, for example, the UE is being handed over, and mayfurther contain the NAS message received by the S-eNB from the EPC. TheNAS message may be received from the EPC before the S-eNB sends ahandover command to the UE, or may be received from the EPC after theS-eNB sends a handover command to the UE.

The receiving, by the EPC, the message sent by the S-eNB may furtherincludes receiving, by the EPC, a handover notification message directlysent by the S-eNB without sending a direct-transfer message by the EPC,and in this case, the EPC directly acquires that the UE is being handedover. In this step, the started retransmission timer may be an S1application part (S1-AP) protocol retransmission timer, or may beanother retransmission timer.

In step 1002, if the handover is successful, the EPC receives thehandover complete message sent by the T-eNB, stops the retransmissiontimer, and sends the NAS message to the UE through the T-eNB when it isnecessary to send the NAS message to the UE.

In step 1003, if the handover fails, when it is necessary to send theNAS message to the UE after the retransmission timer expires, the EPCsends the NAS message to the UE through the S-eNB.

In this step, if the EPC does not receive the handover complete messagefrom the UE after the retransmission timer expires, it is consideredthat the UE is still located in the S-eNB service area. In this case,when it is necessary to send the NAS message to the UE, the EPC sendsthe NAS message to the UE through the S-eNB. Considering the sendingmode, the EPC sends to the S-eNB a direct-transfer message containingthe NAS message to be sent to the UE, and then the S-eNB sends the NASmessage to the UE by using an RRC message downlink direct-transfermessage.

In the second method for NAS message processing during handover in anevolved network according to an embodiment of the present invention, aretransmission timer is disposed in the EPC, and when the handoverfails, the EPC can correctly send the NAS message to the UE when it isnecessary to send the NAS message to the UE after the retransmissiontimer expires. When the handover is successful, the EPC stops theretransmission timer after receiving the handover complete message, andthen sends the NAS message through the T-eNB.

In step 1001, the message which indicates that the UE is being handedover received by the EPC may further contain time information. If thetime is synchronous between the S-eNB and the EPC, the time informationmay be a time point when the S-eNB sends the handover command to the UE,or a time point when the S-eNB receives the direct-transfer message, orreturns the direct transfer failure message, and the like. If the timeis asynchronous between the S-eNB and the EPC, the time information maybe a time interval between sending the handover command to the UE andreceiving the direct-transfer message by the S-eNB. In this case, instep 1001, a time limit of the retransmission timer may be determinedaccording to the time information, and then the retransmission timer isstarted, so as to accurately determine the time limit of theretransmission timer.

A preferred embodiment is provided for the second method for NAS messageprocessing during handover in an evolved network. FIG. 8 shows a flow ofa preferred embodiment of the flow shown in FIG. 7, which is aprocessing flow when the handover fails, and includes the followingsteps.

In step 1101, the UE receives a handover command message sent by theS-eNB, and the message instructs the UE to complete the handoverprocess.

In step 1102, the EPC sends the direct-transfer message to the S-eNB,and the direct-transfer message contains the NAS message to be sent tothe UE.

In step 1103, the S-eNB found that the UE is no longer located in aservice area of the S-eNB, and sends the direct transfer failure messageor direct transfer response message to the EPC, and the direct transferfailure message or direct transfer response message contains a causevalue and time information. The direct transfer failure message ordirect transfer response message may further contain the NAS messagereceived by the S-eNB from the EPC. The NAS message may be received fromthe EPC before the S-eNB sends a handover command to the UE, or may bereceived from the EPC after the S-eNB sends a handover command to theUE.

In step 1104, if the message contains the time information, according tothe time information carried in the direct transfer failure message ordirect transfer response message and based on the experience value, theEPC determines a time length of the handover process of the UE, thusdetermining a time limit of the retransmission timer, starting theretransmission timer, and stopping sending the NAS message temporarily.

In step 1105, the S-eNB detects that the handover fails, or detectsother abnormal situations.

In step 1106, the S-eNB initiates a handover canceling flow to theT-eNB.

In step 1107, the retransmission timer in the EPC expires.

In step 1108, when it is necessary to send the NAS message to the UE,the EPC sends the direct-transfer message to the S-eNB, and thedirect-transfer message contains the NAS message to be sent to the UE.

In step 1109, the S-eNB sends the NAS message to the UE by using an RRCmessage downlink direct-transfer message.

Step 1102 may be performed before step 1101, that is, there is no strictsequence relation between step 1101 and step 1102.

Step 1106 is an optional step, and there is no strict sequence relationbetween step 1106 and steps 1107-1108.

In step 1103, the direct transfer failure message or direct transferresponse message sent to the EPC by the S-eNB not only contains thecause value, but also contains the time information. A message format ofthe direct transfer failure message or direct transfer response messageis listed in Table 3.

TABLE 3 Type Cell/Group Name Reference Symbol Description Message TypeMandatory MME Application Mandatory Integer, Indicating a receiving PartProtocol String end of messages Identifier ENodeB Identifier OptionalInteger, Indicating the identifier String of the eNodeB Cause OptionalInteger, Cause value Enumerated Time Information Mandatory Integer, Timeinformation String Time Stamp Optional Integer, Time stamp String TimeInterval Optional Integer Time interval

Similarly, in the flow shown in FIG. 8, after the UE begins to be handedover, the S-eNB directly notifies the EPC that the UE is currently beinghanded over, rather than receiving the direct-transfer message sent bythe EPC and then notifying the EPC that the UE is currently handed overthrough the direct transfer failure message or direct transfer responsemessage. Thus, the flow is simplified.

Next, a method for forwarding an NAS message during handover in anevolved network according to an embodiment of the present invention isdescribed below.

FIG. 9 is a schematic flow chart of a method for NAS message processingduring handover in an evolved network according to an embodiment of thepresent invention.

The flow includes the following steps.

In step 1201, an S-eNB receives an NAS message sent by an EPC. The NASmessage may be received from the EPC before the S-eNB sends a handovercommand message to a UE, or received from the EPC after the S-eNB sendsa handover command message to the UE.

In step 1202, a T-eNB receives the NAS message sent by the S-eNB byusing an X2 interface control protocol message or a tunnel. The S-eNBmay send the NAS message by containing the NAS message in an RRCmessage, for example, an RRC downlink direct-transfer message, or maysend the NAS message directly.

In step 1203, if the handover fails, the S-eNB sends the NAS message tothe UE.

In step 1204, if the handover is successful, the T-eNB sends the NASmessage to the UE.

In the method for NAS message processing during handover in an evolvednetwork according to an embodiment of the present invention, the NASmessage may be borne in the X2 interface control protocol message, andmay be forwarded between the S-eNB and the T-eNB via the X2 interfacecontrol message, or forwarded via a tunnel between the S-eNB and theT-eNB, which are specific implementations for forwarding the NAS messageat the X2 interface.

The above X2 interface control protocol message may have differentalternative forms. By taking an X2-AP control protocol message and aGTP-C control protocol message as examples below, two preferredembodiments of the first method for NAS message processing duringhandover in an evolved network according to an embodiment of the presentinvention are described below.

FIG. 10 is a schematic flow chart of a first preferred embodiment of theflow shown in FIG. 9. The flow shown in FIG. 10 includes the followingsteps.

In step 1301, the UE receives the handover command message sent by theS-eNB, and the message instructs the UE to complete the handoverprocess.

In step 1302, the EPC sends a downlink direct-transfer message to theS-eNB, and the downlink direct-transfer message contains the NAS messageto be sent to the UE.

In step 1303, the S-eNB sends the received NAS message to the T-eNB.

Specifically, the S-eNB sends the received NAS message to the T-eNB in acell format by bearing the NAS message in the X2-AP control protocolmessage. The S-eNB forwards the NAS message by containing the NASmessage in an RRC message, for example, an RRC downlink direct-transfermessage, or forwards the NAS message directly.

In step 1304, the UE sends a handover acknowledgement message to theT-eNB.

In step 1305, the T-eNB sends a handover complete message to the EPC, soas to notify the EPC that the UE has completed the handover process.

In step 1306, the EPC sends a handover complete response message to theT-eNB, so as to confirm that the handover is completed.

In step 1307, the T-eNB sends the NAS message to the UE by using the RRCdownlink direct-transfer message.

In the flow shown in FIG. 10, step 1302 may be performed before step1301.

In the flow shown in FIG. 10, step 1307 may be performed immediatelyafter step 1304 or step 1305.

The X2-AP control protocol message in step 1303 may be an applicationlayer message exclusively added at the X2 interface, and a messageformat of such message is listed in Table 4.

TABLE 4 Type Cell/Group Name Reference Symbol Description Message TypeMandatory S-eNB Identifier Mandatory Indicating a receiving end ofmessages T-eNB Identifier Mandatory Indicating identifier of the T-eNBitself NAS Message Mandatory String Indicating forwarded NAS message

FIG. 11 is a schematic flow chart of a second embodiment of the flowshown in FIG. 9. The flow shown in FIG. 11 includes the following steps.

Steps 1401-1402 are the same as steps 1301-1302, and steps 1404-1407 arethe same as steps 1304-1307.

The difference between the flow shown in FIG. 11 and the flow shown inFIG. 10 lies in that, in step 1403 of FIG. 11, the S-eNB sends thereceived NAS message to the T-eNB, and specifically, the S-eNB sends thereceived NAS message by bearing the NAS message in the GTP-C controlprotocol message. The S-eNB forwards the NAS message by containing theNAS message in an RRC message, for example, an RRC downlinkdirect-transfer message, or forwards the NAS message directly.

The GTP-C control protocol message may be a user plane messageexclusively added at the X2 interface, and a message format of suchmessage is listed in Table 5.

TABLE 5 Type Cell/Group Name Reference Symbol Description Message TypeMandatory Indicating an identifier of a newly-added GTP-C message NASmessage Mandatory Binary Indicating a forwarded String NAS message

In the flow shown in FIG. 9, the T-eNB may further receive the NASmessage sent by the S-eNB via a tunnel. FIG. 12 is a schematic flowchart of the flow shown in FIG. 9, in which a T-eNB further receives anNAS message sent by an S-eNB via a tunnel. The flow shown in FIG. 12includes the following steps.

In step 1501, the T-eNB sends a user plane IP address and a tunnel endpoint identifier corresponding to the T-eNB to the S-eNB, andestablishes a tunnel from the S-eNB to the T-eNB.

In step 1502, the T-eNB receives the NAS message sent by the S-eNB viathe established tunnel. The S-eNB may forward the NAS message bycontaining the NAS message in an RRC message, for example, an RRCdownlink direct-transfer message, or forward the NAS message directly.

In step 1503, if the handover is successful, the T-eNB sends the NASmessage to the UE.

The established tunnel may be a tunnel exclusively configured to forwardan NAS message, or may be a tunnel configured to transmit user data,which is shared for forwarding the NAS message. The differencethere-between lies in that, the tunnel end point identifier sent by theS-eNB to the T-eNB when the tunnel is established is a tunnel end pointidentifier configured to forward the NAS message or a tunnel end pointidentifier configured to transmit the user data. Thus, depending upondifferent tunnel end point identifiers, different tunnels arerespectively established. By taking the above two tunnels as examples,two preferred embodiments of the second method for NAS messageprocessing during handover in an evolved network according to anembodiment of the present invention are illustrated below.

The above established tunnel is a unidirectional tunnel from the S-eNBto the T-eNB. If the handover process fails, the T-eNB may furtherreturn the NAS message to the S-eNB, and in this case, a tunnel from theT-eNB to the S-eNB is further required.

FIG. 13 is a schematic flow chart of a first preferred embodiment of theflow shown in FIG. 12. The flow shown in FIG. 13 includes the followingsteps.

In step 1601, the S-eNB sends a handover request message to the T-eNB.

If the failure of the handover process is considered in this flow, theT-eNB returns the NAS message to the S-eNB. At this time, the handoverrequest message in step 1601 may contain a user plane IP address of theS-eNB and a tunnel end point identifier configured to forward the NASmessage.

In step 1602, the T-eNB sends a handover request response message to theS-eNB, and the message contains a user plane IP address of the T-eNB anda tunnel end point identifier configured to forward the NAS message.

Through steps 1601-1602, a NAS forwarding tunnel is established, whichmay be a unidirectional tunnel or a bi-directional tunnel.

In step 1603, the UE receives the handover command message sent by theS-eNB, and the message instructs the UE to complete the handoverprocess.

In step 1604, the EPC sends a downlink direct-transfer message to theS-eNB, and the downlink direct-transfer message contains the NAS messageto be sent to the UE.

In step 1605, the S-eNB sends the NAS message to the T-eNB via the NASmessage forwarding tunnel established through steps 1601 and 1602. TheS-eNB may forward the NAS message by containing the NAS message in anRRC message, for example, an RRC downlink direct-transfer message, orforward the NAS message directly.

In step 1606, the UE sends a handover acknowledgement message to theT-eNB.

In step 1607, the T-eNB sends a handover complete message to the EPC, soas to notify the EPC that the UE has completed the handover process.

In step 1608, the EPC sends a handover complete response message to theT-eNB, so as to confirm that the handover is completed.

In step 1609, the T-eNB sends the NAS message to the UE by using an RRCmessage downlink direct-transfer message.

Step 1609 may be performed immediately after step 1606 or step 1607.

In the above flow, if the handover fails, the T-eNB may return the NASmessage to the S-eNB via the bi-directional tunnel established throughsteps 1601-1602, and then the S-eNB sends the NAS message to the UE.

FIG. 14 is a schematic flow chart of a second preferred embodiment ofthe flow shown in FIG. 12. The flow shown in FIG. 14 includes thefollowing steps.

In step 1701, the S-eNB sends a handover request message to the T-eNB.

If the failure of the handover process is considered in this flow, theT-eNB returns the NAS message to the S-eNB. At this time, the handoverrequest message in step 1701 may contain a user plane IP address of theS-eNB and a tunnel end point identifier for forwarding the NAS message.

In step 1702, the T-eNB sends a handover request response message to theS-eNB, and the message contains a user plane IP address of the T-eNB anda tunnel end point identifier for transmitting user data.

Through steps 1701-1702, a user data transmitting tunnel is established,which may be a unidirectional tunnel or a bidirectional tunnel.

Steps 1703-1704 are the same as steps 1603-1604.

In step 1705, the S-eNB sends the NAS message to the T-eNB via the userdata transmitting tunnel established through steps 1701 and 1702. TheS-eNB may forward the NAS message by containing the NAS message in anRRC message, for example, an RRC downlink direct-transfer message, orforward the NAS message directly. Steps 1706-1709 are the same as steps1606-1609.

Step 1709 may be performed immediately after step 1706 or step 1707.

In the flow shown in FIG. 14, the S-eNB forwards the NAS message to theT-eNB via the user data transmitting tunnel. Before the NAS message isforwarded, a label needs to be added to the NAS message, so as to enablethe T-eNB to identify messages transmitted via the same user datatransmitting tunnel, thereby identifying the user data and the NASmessage. The label may be added in various different ways, for example,adding a label field in a header of the GTP-U protocol.

The above user data transmitting tunnel for forwarding the NAS messagemay be one of a plurality of user data transmitting tunnels establishedbetween the S-eNB and the T-eNB. When a certain tunnel is selected forforwarding the NAS message while transmitting user data, variousselection manners may be adopted, for example, selecting a tunnelaccording to a sequence, selecting a tunnel according to load sharing,or selecting a tunnel randomly, and the like.

In the above flow, if the handover fails, the T-eNB returns the NASmessage to the S-eNB via the bi-directional tunnel established throughsteps 1801-1802, and then the S-eNB sends the NAS message to the UE.

In the flow shown in FIG. 12, when the handover fails, the S-eNB sendsthe NAS message to the UE, which particularly includes twoimplementation modes. FIG. 15 is a schematic flow chart of the firstpreferred embodiment of the S-eNB sending an NAS message to a UE whenthe handover fails in the flow shown in FIG. 12. The flow shown in FIG.15 includes the following steps.

In step 1801, the S-eNB makes a backup of the NAS message sent to the UEby the EPC.

In step 1802, if the handover fails, the S-eNB sends the backup of theNAS message to the UE.

In this preferred embodiment, the S-eNB makes a backup of the NASmessage, and when the handover fails, the S-eNB sends the backup of theNAS message to the UE, thereby realizing the effect of correctly sendingthe NAS message to the UE when the handover fails.

Before the S-eNB sends the backup of the NAS message to the UE, theS-eNB initiates a handover canceling flow to the T-eNB.

FIG. 16 is a schematic flow chart of the second preferred embodiment ofthe S-eNB sending an NAS message to a UE when the handover fails in theflow shown in FIG. 12. The flow shown in FIG. 16 includes the followingsteps.

In step 1901, the S-eNB receives the NAS message sent to the UE by theEPC, and sends the NAS message to the T-eNB.

In step 1902, if the handover fails, the S-eNB receives the NAS messagesent by the T-eNB.

In step 1903, the S-eNB sends the NAS message to the UE.

In this preferred embodiment, when the UE is being handed over, theS-eNB forwards the received NAS message to the T-eNB. If the handoverfails, the T-eNB further forwards the NAS message back to the S-eNB, andthen the S-eNB sends the NAS message to the UE. When the handover fails,the NAS message is forwarded between the S-eNB and the T-eNB, therebyrealizing the effect of correctly sending the NAS message to the UE.

Before the S-eNB receives the NAS message sent by the T-eNB, the S-eNBfurther initiates a handover canceling process to the T-eNB.

Next, an apparatus for NAS message processing during handover in anevolved network according to an embodiment of the present invention isdescribed below, which includes an eNodeB and an MME in an EPC, in whichthe MME in the EPC further includes two circumstances.

FIG. 17 is a schematic structural view of a first type of MME in an EPCaccording to an embodiment of the present invention. The MME includes amessage transceiver module 2001 and an execution module 2002.

The message transceiver module 2001 is configured to receive a message,which indicates that a UE is being handed over, sent by an S-eNB, andtransmit the message to the execution module 2002; and receive amessage, which indicates that the UE returns to an S-eNB service area,sent by the S-eNB when the handover fails, and transmit the message tothe execution module 2002.

The execution module 2002 is configured to receive the message, whichindicates that the UE is being handed over, transmitted by the messagetransceiver module 2001, and buffer an NAS message to be sent to the UE;and receive the message, which indicates that the UE returns to theS-eNB service area, transmitted by the message transceiver module 2001,and send to the S-eNB the NAS message to be sent to the UE when it isnecessary to send the NAS message to the UE.

The first type of MME in the EPC according to an embodiment of thepresent invention acquires that the UE is being handed over throughreceiving the message which indicates that the UE is being handed oversent by the S-eNB, so as to buffer the NAS message to be sent to the UE.When the handover fails, the MME receives the message, which indicatesthat the UE returns to the S-eNB service area, sent by the S-eNB, andfurther sends the NAS message to the UE through the S-eNB when it isnecessary to send the NAS message to the UE, thereby realizing theeffect of correctly sending the NAS message to the UE when the handoverfails.

The message transceiver module 2001 is further configured to receive aUE handover complete message sent by the T-eNB when the handover issuccessful, and transmit the message to the execution module 2002. Theexecution module 2002 is further configured to receive the UE handovercomplete message sent by the T-eNB and transmitted by the messagetransceiver module when the handover is successful, and send the NASmessage to the UE when it is necessary to send the NAS message to theUE.

Therefore, the MME in the EPC according to an embodiment of the presentinvention can not only send the NAS message to the UE correctly throughthe S-eNB if it is necessary to send the NAS message to the UE when thehandover fails, but also send the NAS message to the UE correctlythrough the T-eNB if it is necessary to send the NAS message to the UEwhen the handover is successful.

FIG. 18 is a schematic structural view of a second type of MME in an EPCaccording to an embodiment of the present invention. The MME includes acontrol module 2101, a retransmission timer 2103, and an executionmodule 2104.

The control module 2101 is configured to receive a message, whichindicates that a UE is being handed over, sent by an S-eNB, and startthe retransmission timer 2103;

receive a handover complete message sent by a T-eNB, and stop theretransmission timer 2103.

The execution module 2104 is configured to send an NAS message to theS-eNB according to a timing result of the retransmission timer 2103 whenit is necessary to send the NAS message to the UE after theretransmission timer 2103 expires, and send the NAS message to the T-eNBwhen it is necessary to send the NAS message to the UE after theretransmission timer 2103 is stopped.

The second type of MME in the EPC according to an embodiment of thepresent invention acquires that the UE is being handed over throughreceiving the message which indicates that the UE is being handed oversent by the S-eNB, and starts the retransmission timer. When it isnecessary to send the NAS message to the UE after the retransmissiontimer expires, the MME further sends the NAS message to the UE throughthe S-eNB. When the handover is successful, the MME stops theretransmission timer, and sends the NAS message to the UE through theT-eNB, thereby realizing the effect of correctly sending the NAS messageto the UE when the handover is successful or when the handover fails.

The retransmission timer 2103 may be an S1 interface application partprotocol retransmission timer.

The message which indicates that the UE is being handed over received bythe control module 2101 contains time information, and in this case, theMIME further includes a calculation control module 2102 configured toresolve the time information and calculate a time limit of theretransmission timer 2103 according to the time information, and thentransmit the calculating result to the control module 2101.

If the message which indicates that the UE is being handed over containsthe time information, the MIME may accurately determine the time limitof the retransmission timer according to the time information.

Finally, three eNodeBs provided according to an embodiment of thepresent invention are described below in detail. FIG. 19 is a schematicstructural view of a first eNodeB according to an embodiment of thepresent invention. The eNodeB includes a detecting module 2201, ahandover processing module 2202, and an NAS message forwarding module2203.

The detecting module 2201 is configured to detect an abnormal statusduring a handover of a UE, and send a detecting result to the handoverprocessing module 2202.

The handover processing module 2202 is configured to send a messagewhich indicates that the UE is being handed over to an EPC; and send tothe EPC a message about a service area where the UE currently belongs toaccording to a detecting result sent by the detecting module 2201 whenthe handover of the UE fails.

The NAS message forwarding module 2203 is configured to receive the NASmessage sent by the EPC and forward the NAS message to the UE.

In practical applications, the eNodeB may be an S-eNB or a T-eNBdepending upon the specific application situation. Therefore, the firsteNodeB provided according to an embodiment of the present inventionincludes the functions of both the S-eNB and the T-eNB.

The first eNodeB provided according to an embodiment of the presentinvention sends to the EPC the message about the service area where theUE currently belongs to when the handover fails, so as to enable the EPCto correctly send the NAS message to the UE according to the abovemessage.

In practical applications, the eNodeB may be an S-eNB or a T-eNBdepending upon the specific application situation. Therefore, the firsteNodeB provided according to an embodiment of the present inventionincludes the functions of both the S-eNB and the T-eNB.

FIG. 20 is a schematic structural view of a second eNodeB according toan embodiment of the present invention. The eNodeB includes a detectingmodule 2301, a time information module 2302, a handover processingmodule 2303, and an NAS message forwarding module 2304.

The detecting module 2301 is configured to detect an abnormal statusduring handover of a UE, and send a detecting result to the handoverprocessing module 2303.

The time information module 2302 is configured to send time informationcorresponding to the handover of the UE to the handover processingmodule 2303 according to a processing result of the handover processingmodule 2303.

The handover processing module 2303 is configured to send a messagewhich indicates that the UE is being handed over to an EPC, contain thetime information provided by the time information module 2302 in themessage which indicates that the UE is being handed over; and send tothe EPC a message about a service area where the UE currently belongs toaccording to a detecting result sent by the detecting module 2301 whenthe handover of the UE fails. The handover processing module 2303includes a handover execution module 2305 and a UE position processingmodule 2306. The handover execution module 2305 is configured to send amessage which indicates that the UE is being handed over to the EPC, andcontain the time information provided by the time information module2302 in the message which indicates that the UE is being handed over.The UE position processing module 2306 is configured to send to the EPCa message about a service area where the UE currently belongs toaccording to the detecting result sent by the detecting module 2301 whenthe handover of the UE fails.

The NAS message forwarding module 2304 is configured to receive the NASmessage sent by the EPC, and forward the NAS message to the UE.

The second eNodeB according to an embodiment of the present inventioncontains the time information in the message, which indicates that theUE is being handed over, sent to the EPC, so as to enable the EPC todetermine a time limit of the retransmission timer according to the timeinformation, thereby sending the NAS message correctly when the handoverof the UE fails after the retransmission timer expires.

FIG. 21 is a schematic structural view of a third eNodeB according to anembodiment of the present invention. The eNodeB includes a messagetransceiver module 2401 and an NAS message processing module 2402.

The message transceiver module 2401 is configured to receive an NASmessage to be sent to a UE by an EPC, send an X2 interface controlprotocol message containing the NAS message in the NAS messageprocessing module to another NodeB, or send the received NAS message toanother NodeB via a tunnel; receive the NAS message sent by anothereNodeB by using an X2 interface control protocol message or a tunnel,and send the received NAS message to the UE.

The NAS message processing module 2402 is configured to bear the NASmessage received by the message transceiver module 2401 in the X2interface control protocol message.

The third eNodeB provided according to an embodiment of the presentinvention bears the NAS message in the X2 interface control protocolmessage, and forwards the NAS message between eNodeBs by using the X2interface control message, or forwards the NAS message via a tunnelestablished between the eNodeBs, thereby providing a specificimplementation manner for forwarding the NAS message at the X2interface.

The third eNodeB according to an embodiment of the present inventionfurther includes a tunnel establishing module 2403 configured to receivea user plane IP address and a tunnel end point identifier correspondingto another eNodeB, and send a user plane IP address and a tunnel endpoint identifier corresponding to the third eNodeB itself to the othereNodeB, thereby establishing an NAS forwarding tunnel or a user datatransmitting tunnel between the third eNodeB itself and the othereNodeB.

If more than one user data transmitting tunnel is established, the thirdeNodeB provided according to an embodiment of the present inventionfurther includes a tunnel selecting module 2404 configured to select onetunnel from the established user data transmitting tunnels to forwardthe NAS message. The eNodeB further includes a label adding module 2405configured to add a label to the NAS message when the NAS message issent to another eNodeB via the established user data transmittingtunnel. The addition of the label aims at enabling the eNodeB tocorrectly identify the received NAS message when the NAS message and theuser data share the user data transmitting tunnel.

The third eNodeB provided according to an embodiment of the presentinvention further includes a backup module 2406 configured to make abackup of the NAS message to be sent to the UE received by the messagetransceiver module 2401. By adding the backup module 2405, if thehandover fails, the eNodeB can send the backup of the NAS message to theUE.

The three eNodeBs provided in an embodiment of the present inventionrespectively includes the functions of the eNodeB serving as both anS-eNB and a T-eNB.

FIG. 22 is a schematic structural view of an MME according to anembodiment of the present invention. The MME includes a message sendingmodule 2501 and a message receiving module 2502.

The message sending module 2501 is configured to enable an EPC to send adirect-transfer message to an S-eNB, and the direct-transfer messagecontains an NAS message to be sent by the EPC to a UE.

The message receiving module 2502 is configured to enable the EPC toreceive a message, which indicates that the UE is being handed over,sent by the S-eNB, and the message which indicates that the UE is beinghanded over is a direct transfer failure message or direct transferresponse message containing a cause value and an NAS message that failsto be sent.

Furthermore, the MME further includes a timer start module 2503 and atimer stop module 2504.

The timer start module 2503 is configured to enable the EPC to start aretransmission timer. At this time, the message sending module 2501 isconfigured to enable the EPC to send the NAS message to the UE throughthe S-eNB when it is necessary to send the NAS message to the UE afterthe retransmission timer expires if the handover fails.

The timer stop module 2504 is configured to enable the EPC to receive ahandover complete message sent by a T-eNB, and stop the retransmissiontimer. At this time, the message sending module 2501 is configured toenable the EPC to send the NAS message to the UE through the T-eNB whenit is necessary to send the NAS message to the UE.

Through the method and the apparatus for NAS message processing duringhandover in an evolved network provided according to the embodiments ofthe present invention, an EPC is notified that the UE is currently beinghanded over, so that the EPC buffers an NAS message to be sent to theUE. If the handover fails, the S-eNB sends a message which indicatesthat the UE returns to an S-eNB service area to the EPC, so as to enablethe EPC to send the NAS message to the UE correctly. Alternatively, aretransmission timer is set, and the EPC is notified that the UE iscurrently being handed over, so that the EPC starts the retransmissiontimer. If the handover fails, the EPC may send the NAS message to the UEcorrectly through the S-eNB after the retransmission timer expires. Ifthe handover is successful, the EPC may stop the retransmission timerand send the NAS message to the UE through the T-eNB. Alternatively, theNAS message is forwarded to the T-eNB via an X2 interface controlprotocol or a tunnel, thereby providing specific implementation forforwarding the NAS message via the X2 interface.

The above descriptions are merely exemplary embodiments of the presentinvention, and not intended to limit the scope of the present invention.Any modification, equivalent replacement, or improvement made withoutdeparting from the spirit and principle of the present invention shouldfall within the scope of the present invention.

What is claimed is:
 1. A communication method, comprising: sending, by acore network device, a first message to a radio access network node thatincludes a non-access stratum (NAS) message; and receiving, by the corenetwork device, a second message from the radio access network node thatincludes the NAS message and cause information indicating a handover istriggered.
 2. The method according to claim 1, further comprising:starting, by the core network device, a retransmission timer.
 3. Themethod according to claim 1, further comprising starting aretransmission timer in response to the receiving of the second message.4. The method according to claim 2, further comprising: determining, bythe core network device, the retransmission timer has expired and thehandover has failed; and sending, by the core network device, the NASmessage to user equipment through the radio access network node.
 5. Themethod according to claim 1, further comprising: buffering, by the corenetwork device, the NAS message in response to the receiving of thesecond message.
 6. The method according to claim 1, further comprising:sending, by the radio access network node, a third message to the corenetwork device, the third message indicating that user equipment is in aservice area of the radio access network node; receiving, by the radioaccess network node, the NAS message from the core network device; andsending, by the radio access network node, the NAS message to the userequipment.
 7. The method according to claim 1, further comprising:sending, by the radio access network node, a handover command to userequipment after receiving the first message.
 8. The method according toclaim 1, wherein the first message is a direct transfer message.
 9. Themethod according to claim 8, wherein the second message is one of adirect transfer failure message or a direct transfer response message.10. The method according to claim 1, wherein the radio access networknode is a source radio access network node that is engaged in thehandover.
 11. The method according to claim 1, wherein the core networkdevice is a mobility management device.
 12. An apparatus, comprising: aprocessor; and a memory coupled to the processor and configured to storeinstructions, that, when executed by the processor, cause the apparatusto: send a first message to a radio access network node that includes anon-access stratum (NAS) message; and receive a second message from theradio access network node that includes the NAS message and causeinformation indicating a handover is triggered.
 13. The apparatusaccording to claim 12, wherein the instructions when executed by theprocessors, further cause the apparatus to: start a retransmissiontimer.
 14. The apparatus according to claim 12, wherein the instructionswhen executed by the processors, further cause the apparatus to: startthe retransmission timer in response to the receiving of the secondmessage.
 15. The apparatus according to claim 13, wherein theinstructions when executed by the processors, further cause theapparatus to: determine the retransmission timer has expired and thehandover has failed; and send the NAS message to user equipment throughthe radio access network node after determining the retransmission timerhas expired and the handover has failed.
 16. The apparatus according toclaim 12, wherein the instructions when executed by the processors,further cause the apparatus to: buffer the NAS message in response tothe receiving of the second message.
 17. The apparatus according toclaim 12, wherein the first message is a direct transfer message. 18.The apparatus according to claim 17, wherein the second message is adirect transfer failure message or a direct transfer response message.19. The apparatus according to claim 12, wherein the apparatus is amobility management device.
 20. The apparatus according to claim 12,wherein the radio access network node is a source radio access networknode engaged in the handover.